Related art of the present invention is found as a shaft seal device 100 as shown in FIG. 5.
A case 101 of the shaft seal device 100 shown in FIG. 5 is closely inserted and fixed in an inner circumference of a housing 110 through an O-ring 106. On an inner circumference of the casing 101 there are arranged an elastomer lip member 102 and a reinforcement ring 103 which supports the elastomer lip member 102 from its rear side.
In addition, on a rear side of the reinforcement ring 103 which is a side opposite to a sealing object fluid, a resin lip member 104 and a back-up ring 105 which is additionally provided on the rear of the resin lip member 104 and supports the rear are disposed. Each outer diameter portion of the elastomer lip member 102, the reinforcement ring 103, the resin lip member 104 and the back-up ring 105 are securely held onto an inner circumference of the casing 101.
In the shaft seal device 100 of this kind, the elastomer lip member 102 has pumping threads 102b which cause a pumping action in a direction which pushes back the sealing object fluid according to the rotation of a rotary shaft 120 and are formed on an inner circumferential surface of a seal lip portion 102a of an inner diameter side extending to the inner space of machine S1 side. On the other hand, the resin lip member 104 has pumping threads 104b which pushes back the fluid toward the elastomer lip member 102 side when the shaft 120 rotates and are formed on an inner circumferential surface of its seal lip portion 104a. 
The pumping threads 104b in the seal lip portion 104a of the resin lip member 104 are formed at only around a front end of a sliding surface with the rotary shaft 120. This is because there is a need for preventing the fluid from leaking toward an atmosphere S2 side after passing the pumping threads 104b when the rotary shaft 120 stops.
In the shaft seal device 100 of this kind, under a high pressure condition in which the fluid pressure of the inner space of machine S1 is at least 1 MPa, the resin lip member 104 receives an influence of the pressure, thus its section is deformed into an L-shape.
A stress of the front end portion of the seal lip portion 104a in the deformation process is relatively small by the presence of the pumping threads 104b, and a stress generated in the vicinity of a bent portion 104c in which the pumping threads 104b are not formed is relatively large.
Therefore a maximum portion of a surface pressure acted on the outer circumferential surface of the rotary shaft 120 is locally distributed toward the bent portion 104c side. Accordingly, the inner circumferential surface in the vicinity of the bent portion 104c is easily worn.
And the front end portion in which the pumping threads 104b are formed causes a floating deformation on the outer circumferential surface of the rotary shaft 120. As a result, the pumping action of the pumping threads 104b for blocking a fluid leakage is damaged and a sealing capability during the rotary operation is lowered.
Further, the elastomer lip member 102 and the resin lip member 104 are arranged in close proximity of each other. If a sliding surface of the resin lip member 104 is pressed against the rotary shaft 120 and a sliding friction causes a generation of substantial heat, the heat generated is transferred to the elastomer lip member 102.
A similar heat generation is resulted if a high pressure due to the sealing fluid presses the elastomer lip member 102 against the rotary shaft 120. This heat then causes softening of the seal lip portion 102a of the elastomer lip member 102 and the seal lip portion 104a of the resin lip member 104. In particular, a progress of wear in the seal lip portion 102a causes a decrease in the seal capability.
Wear of the seal lip portion 102a of the elastomer lip member 102 and the seal lip portion 104a of the resin lip member 104 also causes wear particles to stick onto the sliding surfaces of the individual seal lip portions 102a, 104a, thus the seal capability is damaged.
In case of a conventional rotary shaft 120, the seal lip portion 102a of the elastomer lip member 102 and the seal lip portion 104a of the resin lip member 104 tend to be quickly worn during the rotation of the rotary shaft 120 wherein the seal lip portions 102a, 104a are firmly pressed against the rotary shaft 120. On the other hand, the rotary shaft 120 which is a kind of machine component embedded inside a machine assembly unit is not only expensive but also hard to be replaced. That is, when the seal surfaces of the seal lip portion 102a of the elastomer lip member 102 and the seal lip portion 104a of the resin lip member 104 are subjected to a sliding movement relative to the worn rotary shaft 120, wear of the both seal surfaces is further accelerated and, as a result, the seal capability of the shaft seal device is decreased.
The present invention is introduced to alleviate the above mentioned problems. A primary technical goal which this invention tries to achieve is to improve a seal capability of various rotary machines even under a circumstance wherein a rotary shaft repeats stop and go motions or a fluid pressure randomly changes between high pressure and low pressure.
Another technical goal is to prevent the seal capability from being damaged as the result of softening of an end face portion of a rubber-made lip member which is caused by a transfer of a frictional heat from a resin-made seal lip member in operation.
Yet another goal is to achieve low energy consumption by means of reducing sliding resistance of the seal lip member and the end face lip member and to simplify the assembly and maintenance process of the seal device.